Technical Field
This invention generally relates to gels having tack-free coatings and, more specifically, to methods for manufacturing gels having a permanent tack-free coating. Such gels are particularly useful when incorporated into surgical devices such as access ports.
Description of the Related Art
A “gel” is often defined as a semisolid condition of a precipitated or coagulated colloid. Despite its derivation from the Latin word gelare “to freeze,” gels differ widely in their fluid/solid characteristics, ranging from more fluid gels, such as those found in gel toothpastes, to more solid gels, such as those used in bicycle seat pads.
Gels tending toward the “solid” end of the spectrum are commonly used to facilitate load distribution. Gels enhance this function by offering a high degree of compliance, which basically increases the amount of area available to support a load. With an increased area of support, the load is accommodated at a considerably reduced pressure. Particularly where the human body is involved, a reduced pressure is desirable in order to maintain capillary blood flow in body tissue. It is with this in mind that gels are commonly used for bicycle seats, wrist pads, insole supports, as well as elbow and shoulder pads.
Gels have been of particular interest in the formation of seals, where the high compliance and extensive elongation of the gel are of considerable value. Such is the case with seals used in trocars and other surgical access devices, including access ports, in which a seal must be formed both in the presence of a surgical instrument (or surgeon's hand) and in the absence of a surgical instrument.
In general, an access device is a surgical device intended to provide access for surgical instruments across a body wall, such as the abdominal wall, and into a body cavity, such as the abdominal cavity. Often, the body cavity is pressurized with a gas, typically carbon dioxide, to enlarge the operative volume of the working environment. Under these conditions, the access device must include appropriate seals to inhibit loss of the pressurizing gas, both with and without a surgical instrument disposed through the seal. Seals formed from a gel material provide a high degree of compliance, significant tear strength and exceptional elongation and thus are particularly useful in access ports.
While the advantageous properties of gels have made them candidates for many applications, one disadvantage has seriously limited their use. Most gels are extremely tacky. This characteristic alone makes them difficult to manufacture and aggravating to use.
Attempts have been made to produce gels that are naturally non-tacky. Such naturally non-tacky gels, however, are not particularly heat tolerant, as low amounts of heat can rapidly cause the materials to take a set and distort, particularly under compressive loads. This can occur over an extended period of time, for example, even at normal room temperatures.
Attempts have been made to enclose tacky gels in a non-tacky pouch. This has also tended to mask the advantageous properties and to significantly increase manufacturing costs.
Lubricants such as silicone oil have been applied to the surface to reduce tackiness. Unfortunately, these lubricants tend to dry out over time leaving the gel in its natural tacky state.
Powders, including starch, have been applied to the tacky surfaces with results limited in both duration and effect. In addition, the use of a starch based powder as a blocking agent and the application of the blocking agent during production increases the cost of manufacture and may necessitate additional cleaning steps, greatly increasing the manufacturing time for producing powdered gel products.
Starch blocking agents further complicate manufacturing by providing a growth medium for bacteria and other microorganisms. Medical devices incorporating gels are typically irradiated at a higher than normal sterilization dose to compensate for this. However, higher sterilization doses are known to compromise mechanical properties of the device materials. Also, because corn starch is not permanently fused to the gel surface, it is easily removed by wetting, revealing the tacky gel and generating corn starch residue.
As noted above, the best gel materials tend to exhibit surfaces that are very tacky. The use of a tacky gel can make the processes of manufacturing and using gels in seals and access devices extremely difficult. A tacky gel also produces significant drag forces during instrument insertion. Furthermore, the tacky surfaces tend to draw and retain particulate matter during the manufacturing and handling processes. For these reasons it is even more desirable to render the highly tacky gel surfaces non-tacky in the case of medical devices such as access ports and other such devices.